Many attempts have been made to produce compositions to simultaneously clean and prevent staining of toilet bowls due to the deposition of minerals on the surface thereof. Many such attempts have concentrated upon the prevention of the mineral staining of toilet bowls, as described in such patents as U.S. Pat. Nos. 4,302,350; 4,129,423 and 3,303,104. These patents, however, have focused upon staining due to manganese because manganese stains are particularly tenacious and difficult to remove.
None of these compositions, however, appear effective in simultaneously preventing the staining of toilets due to the deposition of calcium compounds such as CaCO.sub.3, magnesium compounds such as MgCO.sub.3, iron compounds such as Fe.sub.2 O.sub.3 and manganese compounds such as MnO.sub.2, which compounds all significantly contribute to the staining of the toilet bowl and/or encrustation at the water line of the toilet bowl. To overcome such problems, it has been discovered by the present inventor that the combination of two polymers, particularly a low molecular weight, water-soluble alkali metal salt of a polyacrylate and a low molecular weight water-soluble copolymer of acrylamide and acrylic acid or a copolymer of acrylic acid with certain acrylic acid esters is capable of inhibiting all of the aforementioned major types of mineral staining in a toilet bowl.
Another problem in formulating such toilet bowl cleaning and/or stain-inhibiting compositions resides in the difficulty of preparing slowly dissolving cakes or pellets which are ordinarily added to the tanks of toilets, so that upon flushing of the toilet, the active ingredients which clean and prevent staining are properly released into the toilet bowl. Such cakes or pellets must be capable of dispensing the active ingredients for preventing sedimentation of the various minerals in the toilet bowl in an even and continuous release over an extended period of time. The formulation of a cake to achieve these results is delicate because one must choose a matrix which is capable of slowly eroding and dispensing the ingredients and yet be capable of lasting for a extended period of time in the toilet tank.
According to the present invention, a slow-dissolving cake has been formulated, which is capable of metering out or dispensing the aforementioned, low molecular weight, water soluble polymers from the toilet tank into the toilet bowl during the flushing operation by formulating such polymers with binders and optionally inorganic salts or weighting agents and surfactants to produce a cake which is slowly eroded so as to dispense the active ingredients into the toilet bowl during each flushing, while at the same time lasting over an extended period of time, i.e., for at least one month or so.